I was recently working on investigating an interesting issue with SSO providers and used Fiddler to monitor the network requests. I did this a couple of times. Then the next time when I launched Fiddler, it offered me to update to the latest version. I let it update to v4.6.2.0.

After that, the magic happened. Several sites that I was trying to access loaded only partly, they looked like the CSS is completely missing. Other sites were complaining about the SSL certificate, and presented me with the usual window in Chrome that says “Be careful, the website may not be what it says it is…etc.”.

If I closed Fiddler the issue went away so obviously Fiddler was the culprit. The problem was that Fiddler was intercepting HTTPS requests but was not using the correct certificates. To fix that, you need to do the following:

Click on Tools > Fiddler Options.

Open the HTTPS tab.

Make sure there is a text saying: “Certificates generated by CertEnroll engine”.

Click on Actions > Reset Certificates. This may take a a couple of seconds.